Purification and characterization of bovine dendritic cells from peripheral blood

Phenotype of bovine mononuclear phagocytes- An update

Studying mononuclear phagocytes by flow cytometry is challenging due to their phenotypic similarities and the high plasticity of monocytic cells. Despite these challenges, significant progress has been made in cattle research through multicolor flow cytometry, transcriptomics of sorted subsets, and single-cell RNA-sequencing. Here, we provide an overview of established and proposed phenotypic classifications in the bovine mononuclear phagocyte system and discuss the challenges of marker discovery.

Precise Delineation and Transcriptional Characterization of Bovine Blood Dendritic-Cell and Monocyte Subsets

A clear-cut delineation of bovine bona fide dendritic cells (DC) from monocytes has proved challenging, given the high phenotypic and functional plasticity of these innate immune cells and the marked phenotypic differences between species. Here, we demonstrate that, based on expression of Flt3, CD172a, CD13, and CD4, a precise identification of bovine blood conventional DC type 1 and 2 (cDC1, cDC2), plasmacytoid DC (pDC), and monocytes is possible with cDC1 being Flt3⁺CD172a^dimCD13⁺CD4⁻, cDC2 being Flt3⁺CD172a⁺CD13⁻CD4⁻, pDC being Flt3⁺CD172a^dimCD13⁻CD4⁺, and monocytes being Flt3⁻CD172a^highCD13⁻CD4⁻. The phenotype of these subsets was characterized in further detail, and a subset-specific differential expression of CD2, CD5, CD11b, CD11c, CD14, CD16, CD26, CD62L, CD71, CD163, and CD205 was found. Subset identity was confirmed by transcriptomic analysis and subset-specific transcription of conserved key genes. We also sorted monocyte subsets based on their differential expression of CD14 and CD16. Classical monocytes (CD14⁺CD16⁻) clustered clearly apart from the two CD16⁺ monocyte subsets probably representing intermediate and non-classical monocytes described in human. The transcriptomic data also revealed differential gene transcription for molecules involved in antigen presentation, pathogen sensing, and migration, and therefore gives insights into functional differences between bovine DC and monocyte subsets. The identification of cell-type- and subset-specific gene transcription will assist in the quest for “marker molecules” that—when targeted by flow cytometry—will greatly facilitate research on bovine DC and monocytes. Overall, species comparisons will elucidate basic principles of DC and monocyte biology and will help to translate experimental findings from one species to another.

Phenotypic and functional analysis of bovine peripheral blood dendritic cells before parturition by a novel purification method

Dendritic cells (DCs) are specialized antigen presenting cells specializing in antigen uptake and processing, and play an important role in the innate and adaptive immune response. A subset of bovine peripheral blood DCs was identified as CD172a⁺/CD11c⁺/MHC (major histocompatibility complex) class II⁺ cells. Although DCs are identified at 0.1%–0.7% of peripheral blood mononuclear cells (PBMC), the phenotype and function of DCs remain poorly understood with regard to maintaining tolerance during the pregnancy. All cattle used in this study were 1 month before parturition. We have established a novel method for the purification of DCs from PBMC using magnetic‐activated cell sorting, and purified the CD172a⁺/CD11c⁺DCs, with high expression of MHC class II and CD40, at 84.8% purity. There were individual differences in the expressions of CD205 and co‐stimulatory molecules CD80 and CD86 on DCs. There were positive correlations between expression of cytokine and co‐stimulatory molecules in DCs, and the DCs maintained their immune tolerance, evidenced by their low expressions of the co‐stimulatory molecules and cytokine production. These results suggest that before parturition a half of DCs may be immature and tend to maintain tolerance based on the low cytokine production, and the other DCs with high co‐stimulatory molecules may already have the ability of modulating the T‐cell linage.

Identification and characterization of equine blood plasmacytoid dendritic cells

Dendritic cells (DC) are antigen-presenting cells that can be classified into three major cell subsets: conventional DC1 (cDC1), cDC2 and plasmacytoid DCs (pDC), none of which have been identified in horses. Therefore, the objective of this study was to identify and characterize DC subsets in equine peripheral blood, emphasizing on pDC. Surface marker analysis allowed distinction of putative DC subsets, according to their differential expression of CADM-1 and MHC class II. Equine pDC were found to be Flt3(+) CD4(low) CD13(-) CD14(-) CD172a(-) CADM-1(-) MHCII(low). The weak expression of CD4 on equine pDC contrasts with findings in several other mammals. Furthermore, pDC purified by fluorescence-activated cell sorting were found to be the only cell subset able to produce large amounts of IFN-α upon TLR9-agonist stimulation. The pDC identity was confirmed by demonstrating high-levels of PLAC8, RUNX2 and TCF4 expression, showing pDC-restricted expression in other mammals.

Phenotypic, ultra-structural, and functional characterization of bovine peripheral blood dendritic cell subsets

Dendritic cells (DC) are multi-functional cells that bridge the gap between innate and adaptive immune systems. In bovine, significant information is lacking on the precise identity and role of peripheral blood DC subsets. In this study, we identify and characterize bovine peripheral blood DC subsets directly ex vivo, without further in vitro manipulation. Multi-color flow cytometric analysis revealed that three DC subsets could be identified. Bovine plasmacytoid DC were phenotypically identified by a unique pattern of cell surface protein expression including CD4, exhibited an extensive endoplasmic reticulum and Golgi apparatus, efficiently internalized and degraded exogenous antigen, and were the only peripheral blood cells specialized in the production of type I IFN following activation with Toll-like receptor (TLR) agonists. Conventional DC were identified by expression of a different pattern of cell surface proteins including CD11c, MHC class II, and CD80, among others, the display of extensive dendritic protrusions on their plasma membrane, expression of very high levels of MHC class II and co-stimulatory molecules, efficient internalization and degradation of exogenous antigen, and ready production of detectable levels of TNF-alpha in response to TLR activation. Our investigations also revealed a third novel DC subset that may be a precursor of conventional DC that were MHC class II⁺ and CD11c⁻. These cells exhibited a smooth plasma membrane with a rounded nucleus, produced TNF-alpha in response to TLR-activation (albeit lower than CD11c⁺ DC), and were the least efficient in internalization/degradation of exogenous antigen. These studies define three bovine blood DC subsets with distinct phenotypic and functional characteristics which can be analyzed during immune responses to pathogens and vaccinations of cattle.

Two functionally distinct myeloid dendritic cell subpopulations are present in bovine blood

Immature myeloid (m)DCs circulating in the blood of cattle have been defined as lineage negative (Lin(-))MHCII(+)CD11c(+)CD205(+) cells. Lin(-)MHCII(+)CD11c(+)CD205(+) mDCs (0.2% blood mononuclear cells) isolated from bovine blood were heterogeneous in cell size and CD205 expression. Using highspeed cell sorting, Lin(-)MHCII(+)CD11c(+)CD205(+) DCs were sorted into CD205(Hi) and CD205(Lo) subpopulations which were phenotypically distinct and differed significantly (P<0.01) in TLR gene expression. CD205(Hi) and CD205(Lo) mDCs were more efficient in macropinocytosis than monocytes and expressed no or little detectable non-specific esterase activity. CD205(Lo) mDCs efficiently activated purified allogeneic T cells and the addition of TLR agonists did not significantly alter this antigen presentation capacity. T cell activation by CD205(Lo) mDCs was associated with differential up-regulation of CD40, CD80, CD86 and TGFβ1 gene expression when compared to CD205(Hi) mDCs. In conclusion, two phenotypically and functionally distinct CD11c(+)CD205(+) mDCs were isolated from blood that had an equal capacity to acquire antigen but markedly different capacities to activate T cells.

Cell mediated innate responses of cattle and swine are diverse during foot-and-mouth disease virus (FMDV) infection: a unique landscape of innate immunity

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Harnessing the innate immunity can protect domestic animals from viruses.

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Innate immune cells have potential capacity to afford protection against infection.

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Understanding the innate and adaptive immunity will aid rational vaccine design.

Pathogens in general and pathogenic viruses in particular have evolved a myriad of mechanisms to escape the immune response of mammalian species. Viruses that cause acute disease tend to bear characteristics that make them very contagious, as survival does not derive from chronicity of infection, but spread of disease throughout the herd. Foot-and-mouth disease virus (FMDV) is one of the most contagious viruses known. Upon infection of susceptible species, cloven-hoofed animals, the virus proliferates rapidly and causes a vesicular disease within 2–4 days. Disease symptoms resolve by 10 days to 2 weeks and in most cases, virus can no longer be detected. Periods of fever and viremia are usually brief, 1–3 days. In vivo control of virus infection and clearance of the virus during and following acute infection is of particular interest. The interaction of this virus with cells mediating the early, innate immune response has been analyzed in a number of recent studies. In most reports, the virus has a distinct inhibitory effect on the response of cells early in infection. Here we review these new data and discuss the dynamics of the interaction of virus with different cell types mediating the immune response to infection.

Mucosal dendritic cell subpopulations in the small intestine of newborn calves

Mucosal dendritic cell development in the newborn is poorly understood despite evidence that distinct DC subpopulations populate individual mucosal surfaces. Therefore, we investigated DC phenotype and distribution in the small intestine of newborn calves. DC phenotype was analyzed using flow cytometry and DC distribution was investigated with immunohistochemistry. Purification of CD11c(Hi)MHC Class II(+) cells confirmed CD11c defined myeloid cells and a comparison of neonatal blood and intestine revealed distinct mucosal DC subpopulations. CD11c(Hi)CD14(+) cells were significantly more abundant in newborn ileum versus jejunum and CD335(+) NK cells were the only lymphoid population significantly different in ileum versus jejunum. Immunohistochemistry revealed unique patterns of myeloid cell distribution within the mucosal epithelium, lamina propria, and submucosa. CD11c(+) cells were present within the jejunal but absent from the ileal intraepithelial compartment. In contrast, CD11b(+) cells were present within the ileal but absent from the jejunal intraepithelial compartment. In conclusion, the neonatal small intestine is populated by diverse myeloid subpopulations and significant differences in regional distribution are established early in life. These observations may have significant implications for the response of the newborn to both commensal microflora and enteric pathogens.

The role of dendritic cells in alphaherpesvirus infections: archetypes and paradigms

Dendritic cells (DCs) play a critical role in orchestrating both innate and adaptive components of the immune system and are therefore of pivotal importance in the initiation of immune responses to control and eliminate viral infections. A major focus of this review is to give an overview on the recent findings that point out the importance of DCs in controlling alphaherpesvirus infections, but also indicate that these viruses have evolved several strategies to inhibit and/or exploit DC functions to delay or escape elimination by the immune system. In addition, we point out the common features and interspecies differences between DCs from man and animal, and discuss the potential use of animal alphaherpesvirus homologues to gain further insights into the interaction between alphaherpesviruses and DCs in their natural virus-host environment. Finally, recent knowledge on the potential of alphaherpesviruses as vectors for DC stimulation and their use for immunotherapy is presented.

Isolation of chicken follicular dendritic cells

The aim of the present study was to isolate chicken follicular dendritic cells (FDC). A combination of methods involving panning, iodixanol density gradient centrifugation, and magnetic cell separation technology made it possible to obtain functional FDC from the cecal tonsils from chickens, which had been infected with Eimeria tenella. CD45- dendritic cells were selected using the specific monoclonal antibody against chicken CD45, which is a marker for chicken leukocytes, but is not expressed on chicken FDC. Isolated FDC were characterized morphologically, phenotypically and functionally. The phenotype of the selected cells was consistent with FDC in that they expressed IgG, IgM, complement factors C3 and B, ICAM-1, and VCAM-1, but lacked cell surface markers characteristic of macrophages, T-, and B cells. Transmission electron microscopy confirmed their characteristic dendritic morphology. In addition, the identity of the FDC was further confirmed by their ability to trap chicken immune complexes (ICs) on their surface, whereas they did not trap naive antigen (ovalbumin) or ICs generated with mammalian immunoglobulins. Co-culturing allogeneic or autologous isolated FDC with B cells resulted in enhanced B cell proliferation and immunoglobulin production. The lack of MHC restriction, a functional characteristic feature of FDC, further reinforces the identity of the isolated cells as chicken FDC.

Limited phenotypic and functional maturation of bovine monocyte-derived dendritic cells following Mycobacterium avium subspecies paratuberculosis infection in vitro

After encountering antigen, dendritic cells (DC) must differentiate into a fully mature phenotype to induce a protective, lasting T cell immunity. Paratuberculosis is a disease caused by the intracellular pathogen Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) and is characterized by a transient cell mediated immune response, that when dissipates correlates to the onset of clinical disease. In order to study the mechanism of early cellular immunity associated with M. paratuberculosis infection, we tested the hypothesis that M. paratuberculosis infected bovine DC have impaired activation and maturation thus are defective in the initiation of a sustainable and protective Th1 immune response locally. Our results demonstrate that M. paratuberculosis infected DC showed decreased endocytosis of ovalbumin, indicating some functional maturation. Co-stimulatory molecules CD40 and CD80 mRNA expression from M. paratuberculosis infected DC was increased over untreated immature DC. M. paratuberculosis infection induced chemokine receptor CCR7 increase in DC, yet CCR5 remained high. MHC II surface expression remained low on M. paratuberculosis infected DC. M. paratuberculosis infection inhibited pro-inflammatory cytokine IL-12 production and promoted IL-10 secretion by bovine DC. Together, our findings showed evidence of phenotypic and functional maturation of DC. However, we did not see the expected antigen presentation via MHC II and cytokine responses as a fully mature DC. This may suggest semi-mature DC phenotype induced by M. paratuberculosis infection.

Characterization of a phenotypically unique population of CD13+ dendritic cells resident in the spleen

Immature dendritic cells (DCs) resident in bovine spleens represent a distinct CD11a(+) CD11c(+) CD13(+) CD172(+) CD205(+) population compared to those circulating in peripheral blood or trafficking via afferent lymph. Upon cytokine-induced maturation, splenic DCs both efficiently present antigen in the stimulation of allogeneic lymphocyte proliferation and recall antigen-specific responses.

Comparison of T Cell Subsets Between Somatic Cloned and Normal Cow

PROBLEM

Somatic cloning technology is beneficial for genetically producing excellent animals. However, many developmental problems of somatically cloned animals have been described. Some of them may cause disorders of the immune system, resulting in the fluctuation of the proportion of white blood cells (WBC), different from that of normal animals in peripheral blood.

METHOD OF STUDY

In Holstein- cloned and normal cows, the fluctuation of granulocytes, monocytes, B cells and T cells, and further T cell subsets (CD4+, CD8+, gammadelta, CD8+gammadelta and WC1+gammadelta T cell) in peripheral blood were analyzed in early lactation stage (ELS) and mid to late lactation stage (MLS) by flow cytometry using specific monoclonal antibodies for cell surface markers.

RESULTS

In both ELS and MLS, there were no significant differences in the proportions of granulocytes, monocytes, B cells and T cells between cloned and normal cows. In T cell subsets, gammadelta and WC1+gammadelta T cells in cloned cows were significantly less frequent than in normal cows in ELS. The decreased proportions of gammadelta and WC1+gammadelta T cells recovered to the level of normal cows in MLS.

CONCLUSIONS

The population of granulocytes, monocytes, B cells and T cells, and T cell subsets except for gammadelta and WC1+gammadelta T cells in cloned cows fluctuated in a manner similar to those of normal cows during lactation. In ELS, the proportions of gammadelta and WC1+gammadelta T cells temporarily declined in cloned cows, suggesting that cloned cows may fall into an immunosuppressive state in ELS.

Identification of bovine dendritic cell phenotype from bovine peripheral blood

Dendritic cells (DCs) are professional antigen presenting cells, which initiate primary immune responses and also play an important role in the generation of peripheral tolerance. There is no reliable method established for the isolation of bovine peripheral blood DCs, and furthermore, the phenotypes and the functions of bovine DCs are still not fully clear. In the present study, we have attempted to identify bovine peripheral blood DCs by negative-selection. In bovine peripheral blood mononuclear cells (PBMC), we have newly characterized the phenotype of DCs, which is CD11c+/CD172a+. These cells display features of myeloid type DCs. In the thymic medulla, CD11c+/CD172a+ cells were also present and CD1+/CD172a+ cells were additionally detected as a population of DCs. The data suggest that one of the bovine DCs phenotypes from PBMC is derived from myeloid lineages lacking a CD1 molecule, which then drift to several tissues, and that they then may express a CD1 molecule upon their functional differentiation.

Fractionation of cell mixtures using acoustic and laminar flow fields

A fractionation method applicable to different populations of cells in a suspension is reported. The separation was accomplished by subjecting the suspension to a resonant ultrasonic field and a laminar flow field propagating in orthogonal directions within a thin, rectangular chamber. Steady, laminar flow transports the cell suspension along the chamber, while the ultrasonic field causes the suspended cells to migrate to the mid-plane of the chamber at rates related to their size and physical properties. A thin flow splitter positioned near the outlet divides the effluent cell suspension into two product streams, thereby allowing cells that respond faster to the acoustic field to be separated from those cells that respond more slowly. Modeling of the trajectories of individual cells through the chamber shows that by altering the strength of the flow relative to that of the acoustic field, the desired fractionation can be controlled. Proof-of-concept experiments were performed using hybridoma cells and Lactobacillus rhamnosus cells. The two populations of cells could be effectively separated using this technique, resulting in hybridoma/Lactobacillus ratios in the left and right product streams, normalized to the feed ratio, of 6.9 +/- 1.8 and 0.39 +/- 0.01 (vol/vol), respectively. The acoustic method is fast, efficient, and could be operated continuously with a high degree of selectivity and yield and with low power consumption. (c) 2004 Wiley Periodicals, Inc.

Culture and characterisation of peripheral blood monocytes and monocyte-derived adherent cells of the tammar wallaby, Macropus eugenii

Monocytes, monocyte-derived adherent cells and dendritic cells all play a role in cellular immunity. In this study, we describe the isolation of monocyte-derived adherent cells and dendritic cells from a model marsupial, the tammar wallaby, Macropus eugenii, and report that in vitro, these cells appear morphologically similar to these cells found in other mammals. The successful culture of marsupial monocyte and dendritic cells was undertaken in serum-free medium which contained lymphocyte conditioned medium as an absolute requirement. This supports the view that similar to cultured dendritic cells from other species reported to date, specific growth factors are required to promote the maturation and differentiation of these cells.

Bovine dendritic cells generated from monocytes and bone marrow progenitors regulate immunoglobulin production in peripheral blood B cells

We examined whether bovine monocyte-derived and bone marrow (BM) dendritic cells (DCs) regulate antibody production in activated peripheral blood B cells. DCs were generated from monocytes and BM progenitors in the presence of bovine recombinant granulocyte/macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4). Monocyte-derived DCs promoted B cells activated by the anti-CD3 triggered CD4(+) T cells or through immunoglobulin M (IgM) receptor to increase the level of IgG secretion. Furthermore, the addition of DCs triggered B cells activated through IgM receptors to produce IgG2 and IgA, thus inducing an isotype switch. BM-derived DCs increased the production of IgG in B cells activated by the anti-CD3 triggered CD4(+) T cells, but unlike monocyte-derived DCs did not have any effect on B cells activated through surface IgM. These data suggest that the regulation of humoral immune responses in cattle depends on the origin of DCs and the mode of B cell activation.

Costimulatory molecule requirement for bovine WC1+gammadelta T cells' proliferative response to bacterial superantigens

We have previously shown that the proliferation of freshly isolated bovine WC1+gammadelta T cells to superantigens (SAgs) including staphylococcal enterotoxin A (SEA), and staphylococcal enterotoxin B (SEB) or toxic shock syndrome type-1 (TSST-1) required the presence of antigen-presenting cells (APC) and the addition of exogenous interleukin (IL)-2. The costimulatory activity provided by molecules expressed on professional APC for the proliferation of gammadelta T cells has not been addressed hitherto. In the present study, we investigated the ability of two selected APC populations, the dendritic cells (DCs) highly expressing CD80 and CD86 molecules (CD80highCD86high) and the monocytes expressing the same molecules at a rather low level (CD80lowCD86low), to stimulate the proliferation of purified bovine WC1+gammadelta T cells to SAgs. DCs were more efficient than monocytes in inducing gammadelta T-cell proliferation, and this response was dependent on exogenous IL-2 in both presentation modes. Stimulating gammadelta T cells with gradual doses of SAgs or concanavalin A (ConA) resulted in similar dose-dependent reaction profiles suggesting a minimal role of the major histocompatibility complex (MHC). However, significant proliferation was already obtained with the starting doses in the presence of DC compared with monocytes, and higher proliferation was reached with DC at optimal doses. Finally, the addition of monoclonal antibody (MoAb) anti-CD86 markedly inhibited SAgs- and ConA-mediated proliferation, whereas MoAb anti-CD80 had no effect. The combination of both anti-CD80 and anti-CD86, however, suppressed this response. These results suggest that bovine gammadelta T-cell proliferation response requires indubitably CD86 costimulation. The role of CD80 molecule seems less clear.

Dendritic cells in cattle: phenotype and function

Dendritic cells are professional antigen presenting cells derived from the bone marrow and distributed throughout body tissues where they are located in sites that are suitable for antigen uptake. They are central to the induction of immune responses in naive animals and thus have become targets in strategies that are aimed at modulating resistance to infection. Studies in cattle have shown that the dendritic cells are phenotypically heterogeneous and that the different phenotypes have different biological properties. The molecular basis for this variation has begun to be investigated and has led to the identification of a member of the SIRPalpha family of signal regulatory proteins (MyD1) on a subset of dendritic cells in afferent lymph. Uptake of antigen by cattle dendritic cells is by a number of mechanisms that can involve endocytosis via clathrin coated pits or via caveolae as well as macropinocytosis.

Functional characterization of equine dendritic cells propagated ex vivo using recombinant human GM-CSF and recombinant equine IL-4

Naive T cells can be activated both in vivo and in vitro by specialized antigen presenting cells, dendritic cells (DC), with potent antigen-specific, immunostimulatory activity. Indeed, DC can provide an extremely powerful and important immunological tool by which to potentiate the immune response for specific recognition of foreign antigens. Until recently, the direct isolation of DC from PBMC required laborious procedures with extremely poor yields (<0.1%). Methods have been developed for the human, lower primate, and murine model systems to propagate large numbers of DC from PBMC or bone marrow ex vivo with various cytokines. However, all other model systems, including equine, still require the laborious isolation procedures to obtain DC. In this study, we have adapted the methods developed for the human system to generate large numbers of equine DC from PBMC precursors using recombinant human GM-CSF and recombinant equine IL-4. Our report is the first documentation of ex vivo generated DC from PBMC in a domesticated animal model system. Equine DC derived from PBMC were rigorously characterized by analyzing morphological, phenotypic, and functional properties and were determined to have similar attributes as DC generated from human PBMC. Equine DC appeared stellate with large projectiles and veils and had cell surface antigens at similar levels as those defined on human and murine DC. Furthermore, functional attributes of the DC included rapidly capturing antigens by pinocytosis, receptor-mediated endocytosis, and phagocytosis, activating naive T cells in a mixed leukocyte reaction to a much greater extent than macrophage or lymphoblasts, presenting soluble and particulate antigen 10-100 fold more effectively to T cells on a per cell basis than macrophage or lymphoblasts, and presenting soluble and particulate antigen to both CD4+ and CD8+ T cells. Taken together, our study provides a framework by which equine DC can now be readily produced from PBMC precursors and presents an impetus for and model by which DC can be simply generated in other animal model systems.

Susceptibility of bovine antigen-presenting cells to infection by bovine herpesvirus 1 and in vitro presentation to T cells: two independent events

The aim of the present study was to develop an in vitro system for presentation of bovine herpesvirus 1 (BHV-1) antigens to bovine T lymphocytes and to characterize the antigen-presenting cells (APC) which efficiently activate CD4(+) T cells. Two approaches were used to monitor the infection of APC by BHV-1 as follows: (i) detection of viral glycoproteins at the cell surface by immunofluorescence staining and (ii) detection of UL26 transcripts by reverse transcription-PCR. The monocytes were infected, while dendritic cells (DC) did not demonstrate any detectable viral expression. These data suggest that monocytes are one site of replication, while DC are not. The capacities of monocytes and DC to present BHV-1 viral antigens in vitro were compared. T lymphocytes (CD2(+) or CD4(+)) from BHV-1 immune cattle were stimulated in the presence of APC previously incubated with live or inactivated wild-type BHV-1. DC stimulated strong proliferation of Ag-specific T cells, while monocytes were poor stimulators of T-cell proliferation. When viral attachment to the surface of the APC was inhibited by virus pretreatment with soluble heparin, T-cell proliferation was dramatically decreased. Unexpectedly, incubation of DC and monocytes with the deletion mutant BHV-1 gD-/-, which displays impaired fusion capacity, resulted in strong activation of T lymphocytes by both APC types. Collectively, these results indicate that presentation of BHV-1 antigens to immune T cells is effective in the absence of productive infection and suggest that BHV-1 gD-/- mutant virus could be used to induce virus-specific immune responses in cattle.